The present invention relates to positively charged membranes in general, and, in particular to positively charged membranes comprising a porous substrate. These membranes are useful in detecting, filtering, and or purifying biomolecules, for example, in ion-exchange chromatography and macromolecular transfer.
Detection, filtration, and purification of biomolecules such as proteins, amino acids, nucleic acids, and endotoxins present in fluids such as biological and pharmaceutical fluids have received considerable attention from the industry recently. Ion exchange membranes, particularly positively charged ion exchanged membranes, have been proposed for these purposes. Some of these ion exchange membranes, although they exhibit affinity or binding towards the biomolecules, are not selective. Thus, for example, these membranes have high non-specific protein binding capacity. In addition, the capacities to bind selected proteins of interest are low. Further, preparation of some of the membranes involves complex chemistries or procedures that can lead to increased material and process costs. For example, the preparation can involve radiation grafting of charged monomers, or involve covalently bonding a positive charge modifying polymer to a porous membrane substrate. Further, controlling the chemistry of some of the membranes, e.g., the degree of crosslinking, is rather difficult and/or labor intensive. There further exists a need for a positively charged membrane that has low non-specific binding for biomolecules. There further exists a need for a positively charged membrane that involves a relatively simple chemistry, and at the same time permits the degree of crosslinking to be controlled with ease.
These advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.
U.S. Pat. No. 4,473,474 discloses a cationic charge modified microporous membrane. The membrane comprises a hydrophilic organic polymeric microporous membrane and a charge modified amount of primary cationic modifying agent bonded to the wetted surfaces of the membrane. The primary charge modifying agent is a water soluble organic polymer having a molecular weight greater than about 1000 wherein each monomer thereof has at least one epoxy group capable of bonding to the surface of the membrane and at least one tertiary amine or quaternary ammonium group. U.S. Pat. No. 4,601,828 discloses a method of transferring macromolecules such as nucleic acid and proteins from a chromatographic substrate to an immobilizing matrix. The immobilizing matrix is a charged modified microporous membrane comprising an organic microporous membrane having a charge modifying amount of a cationic charge modifying agent bonded to the wetted surfaces of the membrane.